In the case when data communication is performed in a wired USB (Universal Serial Bus) system, a user needs to connect an electronic device (hereinafter, which will be called a device) to a host device being a communication object. For example, in the case when image data stored in a digital camera being the device is copied in a computer being the host device, the digital camera is coupled to the computer being a communication object through a USB cable.
The above is the similar in the case when data communication is performed in a wireless USB system as well. Here, a wireless USB is one of standards in high-speed short-range wireless communication, and a specification thereof is disclosed in a wireless USB specification (refer to Non Patent Document 1).
In the wireless USB system, communication is performed at a time division multiple access (TDMA) method, and the host device manages wireless USB channels linked by a time slot scheduling management command (Micro-scheduled Management Command: MMC). The host device allocates a slot (a time slot) in a time division manner thereby performing communication with the coupled device. Information with regard to the slot (an attribute, time and the like) is described in the MMC.
Further, in the wireless USB system, in order to realize device side-led processing, the host device allocates a device notification slot (Device Notification Time Slot: DNTS) in the wireless USB channel. The device side-led processing includes connecting the device, cutting the coupling, shifting to a reduced power mode, or the like. The device notifies the host device of a message matching each processing matter by the allocated device notification slot, and thereby coupling of the device, cutting the coupling, or the like is realized.
In the case when data communication is performed by using the wireless USB system in a home, or the like, there are many cases when an environment in a home or the like is a single host environment where one computer exists as the host device. Therefore, although a user is in particular not aware of connecting the device to the host device being a communication object, the device and the host device being a communication object are coupled appropriately.
However, under a multi-host environment where a computer as the host device exists in a narrow range plurally such as an office environment, there is a possibility that the device and the host device are coupled erroneously. It is considered that, for example, as long as the device is capable of receiving radio waves from another host device not being a communication object even when a user moves the device near by the host device being a communication object, the device transmits a coupling request to the host device not being a communication object thereby being coupled thereto.
The host device provides the device notification slot periodically. A user moves the device to the periphery of the host device (within a communication range formed by wireless radio waves that the host device transmits), and thereby the device may detect the device notification slot that the host device provides. Then, the device transmits the coupling request to the host device by the detected device notification slot, and thereby the device and the host device are coupled without performing a coupling setting and the like particular to a user.
There will be considered a case when a communication range (a communicable range) 102 formed by wireless radio waves that a computer (PC-A) 101 being the host device transmits and a communication range 104 formed by wireless radio waves that a computer (PC-B) 103 being the host device transmits do not overlap with each other as depicted in FIG. 10A. It is set to be in a state where the communication ranges 102 and 104 formed by the wireless radio waves from each of the host devices 101 and 103 do not have a region overlapped with the communication range of the adjacent host device, namely in a state corresponding to the single host environment.
Each of the host devices 101 and 103 provides the device notification slot periodically. A digital still camera (DSC) 106 being the device is located within the communication range 102 therefore being able to detect the device notification slot that the host device 101 provides and perform the coupling request and the like to the host device 101. On the other hand, the device 106 is located outside the communication range 104 therefore not detecting the device notification slot that the host device 103 provides.
Similarly, a printer 105 being the device is located within the communication range 104 therefore being able to detect the device notification slot that the host device 103 provides and perform the coupling request and the like to the host device 103. On the other hand, the device 105 is located outside the communication range 102 therefore not detecting the device notification slot that the host device 101 provides.
On the contrary, as depicted in FIG. 10B, under the environment (the multi-host environment) where the communication ranges 102 and 104 formed by the wireless radio waves from the adjacent host devices 101 and 103 overlap at least one portion, when the device 106 is moved to the region overlapped with the communication ranges 102 and 104, the device 106 may detect the device notification slots from both of the host devices 101 and 103. Accordingly, the device 106 may perform the coupling request and the like to both of the host devices 101 and 103.
In order to connect the device to the targeted host device being a communication object under the multi-host environment where the plural host devices exist in a narrow range, there has been suggested a device in which a narrow region range is set as a communication range formed by wireless radio waves from the host device by using a plurality of directional antennas, and thereby one portable device is indicated from a large number of portable devices existing around the host device to establish coupling with the host device (refer to, for example, Patent Document 1).
Further, there has been suggested a device in which when an inquiry signal is transmitted by varying transmission power in stages and a response signal corresponding to the inquiry signal is received from a partner device, the partner device establishing communication may be selected easily so as to display a list of the partner device (refer to, for example, Patent Document 2).                Patent Document 1: Japanese Patent Application Laid-open No. 2002-16968        Patent Document 2: Japanese Patent Application Laid-open No. 2003-218785        Non Patent Document 1: Wireless Universal SerialBus Specification, Revision 1.0 released May 12, 2005        